1. Field of the Invention
The present invention relates generally to a check valve for the pump of an electronically controlled brake system, such as an anti-lock brake system, a brake traction control system or a vehicle dynamic control system, and, more particularly, to a piston type check valve.
2.Description of the Related Art
In general, an electronically controlled brake system is used to provide powerful and stable braking force by preventing an automobile from skidding. For such electronically controlled brake systems, there have been disclosed an Anti-lock Brake System (ABS) for preventing an automobile from skidding during the application of a brake, a Brake Traction Control System (BTCS) for preventing driving wheels from skidding during the abrupt start or acceleration of an automobile, and a Vehicle Dynamic Control System (VDCS) for maintaining an automobile in a stable state by controlling brake oil pressure using a combination of an ABS and a BTCS.
Such an electronically controlled brake system includes a plurality of solenoid valves for controlling brake oil pressure transmitted to hydraulic brakes mounted on the wheels of an automobile, a low-pressure accumulator and high-pressure accumulator for temporarily storing brake oil removed from the hydraulic brakes, a motor and pump for forcibly pumping brake oil stored in the low-pressure accumulator, and an Electronic Control Unit (ECU) for controlling the operation of the solenoid valves and the motor. The above-described components are enclosed in a compact pump housing made of aluminum.
A conventional check valve for controlling the flow of fluid in a pump for an electronically controlled brake system is depicted in FIG. 1.
FIG. 1 is a sectional view showing a conventional ball-type check valve that is used in the pump of the electronically controlled brake system. The ball-type check valve, as shown in FIG. 1, includes a valve body 3 provided with an inlet 3a, an outlet 3b and a valve seat 3c, a ball 5 adapted to selectively opening and closing the valve seat 3c, a spring seat 7 tightly fitted into the valve body 3, and a spring interposed between the ball 5 and the spring seat 7. The check valve constructed as described above is tightly fitted into a pump housing 1.
Meanwhile, the above-described check valve has the following problems.
First, when the ball 5 moves away from the contact surface of the valve body 3, the ball 5 moves laterally due to the gap between the inner wall 3d of the valve body 3 and the ball 5, so that the operation thereof is unstable, thus causing the discharge pressure value of the outlet 3b to be unstable.
Second, when the ball 5 moves away from the contact surface and then comes into contact with the contact surface, the contact position of the ball 5 may vary due to the movement of the ball 5, so that leakage and variation in opening pressure may occur due to the irregular wear and variation in contact position of the ball 5 during long-term operation.
Third, since the spring 9 is seated on the spherical ball 5, the seating surface of the spring 9 is not stable, so that the function of the spring 9 may be degraded due to the offset of the spring 9, or the function and quality of the check valve may be considerably reduced due to the contact of the spring 9 with the inner wall 3d of the valve body 3.